The present invention relates to a method for compensating flow rate of hydraulic pump and more particularly, a method for compensating a discharge flow rate of hydraulic pump for construction machine in order to remove a dead zone in which the discharge flow rate does not change by operation of an operation lever.
FIG. 1(a, b) are the graphs showing a pump volume and a discharge flow rate of a hydraulic pump in response to an operation amount of an operation lever according to the conventional technology, respectively,
FIG. 1(a)shows that a pump volume of the hydraulic pump in response to a pilot pressure (Pi) applied to the control valve by operation of the operation lever does not vary depending on an engine RPM (Revolutions Per Minute).
As shown in FIG. 1(b), a discharge flow rate (q1×s1) corresponding to a required pump volume (q1) in accordance with an operation amount of the operation lever, and a preset higher engine RPM (s1) represented by the graph (a) differs from a discharge flow rate (q2×s2) of the graph (b) corresponding to a required pump volume (q2) which has been compensated by taking the engine RPM into account, and a preset lower engine RPM (s2).
Accordingly, since the discharge flow rates of the graphs (a, b) are different from each other at a starting point of the operation (point of pilot pressure Pa), the initial sense of operation which is experienced by the operator when the working device like boom gets started becomes different depending on the preset engine RPM.
FIG. 1(c, d) are the graphs showing the pump volume and the discharge flow rate of the hydraulic pump in response to the operation amount of the operation lever according to the another conventional technology, respectively. FIG. 2 is a flow chart. Showing a method for compensating a discharge flow rate of the hydraulic pump according to the conventional technology. In accordance with the conventional technology, a method for compensating the discharge flow rate of the hydraulic pump for a construction machine, the construction machine including a variable displacement hydraulic pump (hereinafter, hydraulic pump) connected to the engine; a hydraulic actuator that drives the working device by operating a hydraulic fluid discharged from the hydraulic pump; a control valve (MCV) installed in a flow path that is connected between the hydraulic actuator and the hydraulic pump; an operation lever (RCV) outputting a signal pressure corresponding to an operation amount; a means for detecting the operation amount of the operation lever; a means for detecting an engine RPM; and a controller for controlling the control valve in response to the signal pressure corresponding to the operation amount and the detected signal corresponding to the engine RPM, the method comprises,
a step of detecting the signal pressure corresponding to the operation amount of the operation lever, and the engine RPM (s10);
a step of presenting a required pump volume (q1) corresponding to the operation amount of the operation lever, and a required pump volume (q2) compensated for the engine RPM (s20);
a step of comparing the required pump volume (q1) with the required pump volume q2 (s30);
a step of controlling the hydraulic pump so that a discharge flow rate corresponds to the operation amount of the operation lever if the reauired pump volume q1 is greater than the reauired pump volume q2 (q1>q2) (s40); and,
a step of controlling the hydraulic pump so that a discharge flow rate corresponds to the flow rate compensated for the engine RPM if the reauired pump volume q1 is smaller than the reauired pump volume q2 (q1<q2) (s50).
According to the conventional method for compensating a flow rate discharged from the hydraulic pump, if the pilot pressure corresponding to the operation amount of the operation lever is inputted to the control valve, the flow rate discharged from the hydraulic pump is set in such a way that, in a state where the engine RPM is low, the required pump volume (q1) corresponding to the operation amount of the operation lever is adjusted to the required pump volume (q2) compensated by the engine RPM as shown in FIG. 1(c).
As shown in FIG. 1(d), since the compensated value of the required pump volume does not depend on the pilot pressure (Pi) given by operation of the operation lever, the discharge flow rate of the hydraulic pump does not change even with of the change in the operation of the operation lever in a state where the operation is operated until pilot pressure (Pc) in a dead zone.
Then, the discharge flow rate of the hydraulic pump abruptly increases at the operation moment (the operation lever is positioned at pilot pressure Pc) of leaving the dead zone. Thus, due to the existence of the dead zone in the operation of the operation lever, the discharge flow rate increases against the operator's intention, making the operation speed of the working device fast and deteriorating the operation sensibility and the workability.
It is desirable to provide a method for compensating, a discharge flow rate of a hydraulic pump of construction equipment, in which the discharge flow rate can be controlled as the operator intends to by removing a dead zone in the operation of the operation lever.
In accordance with an aspect of the present invention, there is provided a method for compensating a discharge flow rate of a hydraulic pump for construction machine equipment including a hydraulic pump connected to an engine; a hydraulic actuator that drives the working device by operating hydraulic fluid; a control valve installed in a flow path of the hydraulic pump; an operation lever outputting the signal pressure corresponding to an operation amount; a means for detecting the operation amount of the operation lever; a means for detecting, an engine rpm; and a controller for controlling the control valve in response to the signal pressure corresponding to the operation amount and the detected signal corresponding to an engine rpm, the method comprising;
detecting the signal pressure corresponding to the operation amount of the operation lever, and the engine rpm;
determining a required discharge volume corresponding to the operation amount of the operation lever and the compensation ratio, and determining a required discharge volume that is compensated for the engine rpm, and controlling a discharge flow rate of the hydraulic pump;
wherein the discharge flow rate is derived from the sum of the required volume corresponding to the operation amount of the operation lever and the calculated volume that is obtained by multiplying the percentile compensation ratio by the difference value between the required volume corresponding to the operation amount of the operation lever and the required volume that is compensated for the engine rpm.
The compensation ratio ranges from 100% when the spool of the control valve begins to shift by the operation of the operation lever to 0% when the discharge flow rate is controlled corresponding to the operation amount, and decreases with the pilot pressure, which means that the ratio is inversely proportional to the pilot pressure.
According to the embodier rent of the present invention having the above-described configuration, a dead zone of the discharge flow rate is avoided in the operation of the operation lever for driving the working device such as excavator, allowing the discharge flow rate to be controlled at the operator's intention and thus improving the operation sensibility and the workability.